There is indirect evidence that at the neuromuscular junction, neural activity regulates both synaptic maintenance and synaptic remodelling by a proteolytic mechanism. More exaggerated but similar proteolytic mechanisms may come into play early in denervation or in disease entities such as anyotrophic lateral sclerosis. The goal of this proposal is to test and expand the hypothesis of neuronal regulation of neuromuscular junctional protelysis, using a short-term model of stimulation-induced proteolysis. They hypothesis is that nerve activitiy brings about secretion or activation of intra-synaptic proteinasses. The short-term consequences of this proteolysis -- to be explored here -- are partial destruction or alteration of synaptic macromolecules (e.g. extracellular matrix, receptors). The long-term consequences -- a subject for later study -- may be alterations in nerve or post-synaptic structure, numbers of functional synaptic molecules, or transmitter release. In the short-term model (based on previous finding), the conditions which maximize, minimize or inhibit proteolysis in curarized and indirectly stimulated nerve muscle preparations will be defined. In the initial experiments, release of fluorescamine-positive amino acids or peptides from stimulated nerve-muscle preparations will be used as an index of stimulation-induced proteolysis. In addition, the likely synaptic proteinase substrates (especially matrix or receptor macromolecules) will be deduced from analysis of proteolytic fragments released into the medium. Finally, the possibility of release of soluble proteolytic enzyme by nerve stimulation will be directly tested. These experiments will provide the basis for exploration of the role of proteolysis in long-term synaptic modulation or in disease entities affecting the motor neuron or nerve=muscle junction.